Field
The present disclosure relates to telecommunications apparatus and methods.
Description of Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Mobile communication systems have evolved over many years from the GSM System (Global System for Mobile communications) to the 3G system and now include packet data communications as well as circuit switched communications. The third generation partnership project (3GPP) is developing a fourth generation mobile communication system referred to as Long Term Evolution (LTE) in which a core network part has been evolved to form a more simplified architecture based on a merging of components of earlier mobile radio network architectures and a radio access interface which is based on Orthogonal Frequency Division Multiplexing (OFDM) on the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) on the uplink.
Although there are situations which benefit from high data rates now supported in wireless telecommunications systems, there are also some situations in which high data rates are not required. Examples include so-called machine type communication (MTC) applications, which are typified by semi-autonomous or autonomous wireless communication devices (i.e. MTC devices) communicating small amounts of data on a relatively infrequent basis. Examples include so-called smart meters which, for example, are located in a customer's house and periodically transmit information back to a central MTC server relating to the customer's consumption of a utility such as gas, water, electricity and so on. Further information on characteristics of MTC-type devices can be found, for example, in the corresponding standards, such as ETSI TS 122 368 V12.4.0 (2014-10)/3GPP TS 22.368 version 12.4.0 Release 12 [1]. Some typical characteristics of MTC type terminal devices/MTC type data might include, for example, characteristics such as low mobility, high delay tolerance, small data transmissions, infrequent transmission and group-based features, policing and addressing.
Because MTC devices typically require only modest communications capabilities they may be provided with reduced capabilities as compared to conventional smartphone type devices to reduce costs. In this respect, MTC devices may also be referred to as reduced capability devices. Reducing costs can be particular important for MTC devices because they can be expected to be deployed widely.
One area where it has been proposed to reduce costs for MTC devices is in respect of their operating bandwidths. Whilst a conventional LTE terminal device might be expected to support operations over a 20 MHz bandwidth, it can be expected MTC devices may only support operations over relatively narrow bandwidths, for example 1.4 MHz has been proposed. That is to say, MTC devices may be narrowband devices. It has also been proposed that MTC devices should support so-called coverage extension/coverage enhancement, for example providing an effective additional 15 dB in signalling power as compared to more conventional terminal devices. This has been proposed because it may be expected that MTC devices will often be in locations which are difficult to reach from a radio perspective, for example in the basement of a building in the case of an MTC device associated with a smart meter.
One approach for providing coverage extension is to rely on repeated transmissions of signalling in multiple subframes. A terminal device may then combine the signalling received for a plurality of repeated transmissions to increase the likelihood of successfully decoding the signalling, e.g. using chase combining/maximal ratio combining techniques. This repeated transmission approach may be applied for control signalling (e.g. sent on a physical downlink control channel such as (E)PDCCH in LTE) and/or other signalling (e.g. sent on a physical downlink shared channel such as PDSCH in LTE).
One draw-back of a repeated transmission approach for providing coverage extension, for example in the context of low-cost MTC terminal devices, is a potential need for increased receiver complexity to allow terminal devices to handle the potential for repeated transmissions, especially in situations where the network has flexibility over the numbers of repetitions in respect of different data transmissions. In some respects these issues can become even more significant for narrowband operations since these limit the ability to support repetitions in the frequency domain, as opposed to the time domain. There is therefore a need for schemes that support coverage enhancement through message repetition which help reduce the hardware requirements associated with receivers.